Japanese numerals

The system of Japanese numerals is the system of number names used in the Japanese language. The Japanese numerals in writing are entirely based on the Chinese numerals and the grouping of large numbers follow the Chinese tradition of grouping by 10,000. Two sets of pronunciations for the numerals exist in Japanese: one is based on Sino-Japanese (on'yomi) readings of the Chinese characters and the other is based on the Japanese yamato kotoba (native words, kun'yomi readings).

There are two ways of writing the numbers in Japanese, in Hindu-Arabic numerals (1, 2, 3) or in Chinese numerals (一, 二, 三). The Hindu-Arabic numerals are more often used in horizontal writing, and the Chinese numerals are more common in vertical writing.

Most numbers have two readings, one derived from Chinese used for cardinal numbers (On reading) and a native Japanese reading used for ordinal numbers (Kun reading), though there are some exceptions (listed below) in which the Japanese version is preferred for both.

Numerals with multiple On readings use the Go-on and Kan-on variants respectively.

* The special reading maru (which means "round" or "circle") is also found. It may be optionally used when reading individual digits of a number one after another, instead of as a full number. A popular example is the famous 109 store in Shibuya, Tokyo which is read as ichi-maru-kyū (Kanji: 一〇九). (It can also be read as 'ten-nine' - pronounced tō-kyū - which is a pun on the name of the Tokyu department store which owns the building.) This usage of maru for numerical 0 is similar to reading numeral 0 in English as oh. It literally means a circle. However, as a number, it is only written as 0 or rei (零^?). Additionally, two and five are pronounced with a long vowel in phone numbers (i.e. にい and ごお nii and goo)

...
Wikipedia